I should also have mentioned that besides the low mid range torque, there are a couple of other problems that are still under review, the main one at present is, as my friend rid967 has alluded to, the MoT emission problems. In short it will not comply as standard. I have contacted Steve Morris directly and he says that if I would like to get the car to the factory, they will 'flash' the ECU, however, I am a little concerned that will effect other areas of the engine performance, so I am just holding fire on that one for a bit.
The other major problem is that the handbrake never really worked properly. MMC decided to use a shorter tunnel mounted lever for some reason, not the vertical fly off version in other trads. and it just didn't bite. I have played with it and my partial fix was to extend the lower section of the lever, below the pivot point, to increase leverage. This now just complies with the MoT requirements, but it is not great, certainly no good if I wanted to perform a handbrake turn!
By the way Kevfitz, the Supersport didn't ever have the 5 link back end with coileovers, and if you remember, they had a real problem with emissions early on too. The mpg readout on the dashboard is also calibrated for US gallons, in realife UK terms I always get over 30 and generally around the 35 mark unless I am really giving it the beans. At low revs. it is beautifully mapped with no jerks or hiccups and is a real pleasure to potter with, it is just the sector between 2000 - 3000 that needs some muscle.
I originally found the rear exit twin tailpipe exhaust system a little noisy and tiring on a run, and changed the silencer for a long straight through Caterham silencer which I just happened to have lying around, (as you do), and without losing any power it brought the noise down to acceptable levels, however I have now replaced it with the original silencer, but removed the long and fairly heavy tailpipe for a short 90 degree side exit tailpipe. Funnily enough this has quietened the exhaust and reduced, but not eliminated, the pops and bangs a tad. Maybe it was the resonance in the longer pipe that made it louder - who knows.
Peters suggestion of the Omex 2.5 Duratec is very valid, and I know from owing a 2.3 Duratec. engined Caterham CSR for 5 years how torquey they are, but it is an expensive option and I think if I was going to change the motor I would rather go for Griffos option, and then swap the Cosworth engine back in at eventual sale time to retain any residual value the ARP4 might have.
As an aside, does anyone know if the story that MMC bought 50 2l Cosworth Duratec engines direct, for a very reasonable sum, have any validity to the conception of the ARP4. I rather like the story and can see how it would fit in the MMC thinking.